Method and apparatus for testing the impedances of geophone channels

Abstract

This application relates to seismic data gathering devices and to testing the impedances of the geophone channels of such devices. The invention includes impressing a test current on each channel to be tested, said current developing a test voltage indicative of the impedance; generating a high reference voltage which corresponds to the maximum acceptable impedance of the channel; generating a low reference voltage which corresponds to the minimum acceptable impedance of the channel; and comparing the test voltage with the reference voltages.

I claim: 
     
       1. An apparatus for testing the impedances of a plurality of geophone channels of a seismic data gathering device, said apparatus comprising: a plurality of current sources which feed test currents into the geophone channels to develop a test voltage across each channel that is proportional to that channel's impedance;   a comparator for each geophone channel, said comparator being connected to each channel to compare the test voltage for that channel with a high reference voltage that is proportional to the maximum acceptable impedance for that channel and with a low reference voltage that is proportional to the minimum acceptable impedance for that channel; and   a simulator for developing the high and low reference voltages for each channel, said simulator being connected to each channel and comprising a first voltage source providing a first voltage which is proportional to the lowest nominal impedance of the geophone channels;   a second voltage source providing a second voltage which is proportional to the highest nominal impedance of the geophone channels;   a first operational amplifier having a first gain setting and a second gain setting and receiving said first voltage at one of its input terminals;   a second operational amplifier having a first gain setting and a second gain setting and receiving said second voltage at one of its input terminals, said first and second gain settings being substantially equal to those of the first operational amplifier;   a voltage divider coupled to the output terminals of the operational amplifiers, said voltage divider providing a series of high reference voltages proportional to the maximum acceptable impedances of the geophone channels when said amplifiers are on their first gain settings and said voltage divider providing a series of low reference voltages proportional to the minimum acceptable impedances of the geophone channels when said amplifiers are on their second settings; and   means connected to said amplifier for controlling the gain settings of the amplifiers,     whereby a measurement is made for each channel whether the impedance of that channel falls within acceptable limits.   
     
     
       2. The apparatus of claim 1, wherein the current sources feed the test currents to the channels substantially simultaneously. 
     
     
       3. The apparatus of claim 1, including also for at least one channel a visual indicator which visually displays the results of the comparisons between the high and low reference voltages and the test voltage, said visual indicator being connected to the comparator. 
     
     
       4. A seismic data gathering device, said device including: a signal recording and computing system, said system having a plurality of input channels;   a plurality of geophone channels, each channel having one or more geophones and a pair of wires, each wire pair being connected to the geophones of that channel;   means for selectively connecting the wire pairs of the geophone channels to distinct input channels of the recording and computing system;   a plurality of current sources of test currents to be fed into the geophone channels to develop a test voltage across each channel that is proportional to the channel's impedance;   means for selectively connecting said current sources to the geophone channels;   a comparator for each channel for comparing the test voltage developed across that channel with a high reference voltage that is proportional to the maximum acceptable impedance for that channel and with a low reference voltage that is proportional to the minimum acceptable impedance for that channel;   means for connecting the comparators to the channels; and   a simulator for developing for each channel the high and low reference voltages, said simulator being connected to each channel and comprising a first voltage source providing a first voltage which is proportional to the lowest nominal impedance of the geophone channels;   a second voltage source providing a second voltage which is proportional to the highest nominal impedance of the geophone channels;   a first operational amplifier having a first gain setting and a second gain setting and receiving said first voltage at one of its input terminals;   a second operational amplifier having a first gain setting and a second gain setting and receiving said second voltage at one of its input terminals, said first and second gain settings being substantially equal to those of the first operational amplifier;   a voltage divider coupled to the output terminals of the operational amplifiers, said voltage divider providing a series of high reference voltages proportional to the maximum acceptable impedances of the geophone channels when said amplifiers are on their first gain settings and said voltage divider providing a series of low reference voltages proportional to the minimum acceptable impedances of the geophone channels when said amplifiers are on their second settings; and   means connected to said amplifiers for controlling the gain settings of the amplifiers.     
     
     
       5. The device of claim 4, said device further comprising a plurality of visual indicators, at least one for every channel and connected to the comparator for its channel, said indicators displaying the results of the comparisons between the high and low reference voltages and the test voltage developed across that channel, whereby, when the current sources are connected to the channels and when the simulator and wires are connected to the comparators, a visual indication is generated for each channel showing whether the impedance of that channel is within acceptable limits.   
     
     
       6. The device of claim 4, wherein said comparators each have two input terminals and an output terminal, one of said input terminals being connected to the simulator and the other of said input terminals being connected to one of the wires of the geophone channel, and the output terminal being connected to the vidual indicator.